Mechanistic Studies of Adamantylacetophenones with Competing Reaction Pathways in Solution and in the Crystalline Solid State,The Journal of Organic Chemistry

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Mechanistic Studies of Adamantylacetophenones with Competing Reaction Pathways in Solution and in the Crystalline Solid State
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2019-08-14 00:00:00 , DOI: 10.1021/acs.joc.9b01720
Vince M. Hipwell ₁ , Miguel A. Garcia-Garibay ₁

Affiliation

Photochemical reactions in crystals occur under conditions of highly restricted molecular mobility such that only one product is generally obtained, even when there are many others that can be observed in the gas phase or in solution. A series of 2-(1-adamantyl)-o-alkyl-acetophenones with γ-hydrogen atoms on both the adamantyl and ortho aromatic groups was selected to determine whether one can engineer and observe competing Norrish type II reaction pathways in the crystalline state. It was shown that excited state competition for hydrogen abstraction between secondary adamantyl and benzylic hydrogens is affected not only by the relative bond dissociation energies but also by the molecular conformation in the crystal. The subsequent fate of the resulting biradical species is determined by competition between radical recombination to form the photoproduct and reverse hydrogen atom transfer to regenerate the starting ketone. Crystallographic information, photoproduct distributions in solution and in the solid state, and the results of multiple mechanistic experiments, including transient absorption spectroscopy in acetonitrile and with nanocrystals suspended in water, are reported. The results demonstrate that it is possible to engineer competing reactions in crystals and that consideration of all of the aforementioned factors is necessary to account for the observed photoproduct selectivity.

中文翻译：

在溶液中和结晶固态中具有竞争性反应途径的金刚烷基苯乙酮的机理研究

晶体中的光化学反应是在分子迁移性受到严格限制的条件下发生的，因此即使在气相或溶液中可以观察到许多其他产物，通常也只能得到一种产物。在金刚烷基和邻位均具有γ-氢原子的一系列2-（1-金刚烷基）-邻烷基苯乙酮选择芳香族基团来确定是否可以设计和观察处于结晶状态的竞争性Norrish II型反应途径。结果表明，在仲金刚烷基氢和苄基氢之间的激发态竞争夺取氢不仅受到相对键解离能的影响，而且还受到晶体中分子构象的影响。通过自由基重组形成光产物与反向氢原子转移以再生起始酮之间的竞争来确定所得双自由基物质的后续命运。报告了晶体学信息，溶液和固态中的光产物分布，以及多种机理实验的结果，包括乙腈中的瞬态吸收光谱法和悬浮在水中的纳米晶体。

更新日期：2019-08-14

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